Depressive disorders are common in patients with Parkinson's disease (PD), affecting as many as half of a cross sectional sample of patients. Notwithstanding the selective and often subtle cognitive deficits previously identified in PD, there are substantive differences in cognitive performance between patients who are depressed and those who are not. It is widely accepted that depression will decrease motivation and attention, thereby impairing performance on many cognitive tasks. It has only recently been proposed that depression selectively impairs performance on tasks classically considered to localize to the frontal lobes. This clinical association in PD of depression and selective cognitive deficits may implicate common neurochemical and neuroanatomical pathways. This study proposes to examine the interaction between changes in regional glucose metabolism, mood, and cognitive function in depressed PD patients treated with the selective serotonin uptake blocker, Fluoxetine. The hypothesis is that mood is well as specific cognitive deficits will improve following treatment with Fluoxetine. Furthermore, specific regional changes in brain glucose metabolism will occur, and will predict clinical improvement in mood state and cognitive performance. This study, using a multidisciplinary design, will focus on the specific interactions between brain chemistry, anatomy, and behavior relevant to the depression identified in patients with PD. To this end, the proposed studies will determine: (1) whether measurements of regional glucose metabolism are a specific marker of depressive state or trait in patients with PD, (2) whether improved performance on some, but not all cognitive tasks accompanies resolution of depressive symptoms, and (3) whether distinct patterns of regional glucose metabolism identify brain regions associated with depression-sensitive and depression-independent cognitive functions. This proposal would be a first step in the mapping of specific anatomical and neurochemical pathways involved in the genesis and recovery from depressive illness in patients with PD.